Sunday, April 17, 2016

How Convergent Science Automates CFD Meshing

Issue #898

by Ralph Grabowski with Rob Kaczmarek

Convergent Science, founded in 1997 by a group of PhD students at the University of Wisconsin-Madison, kept a low profile in Europe for the next 20 years. I'll explain why you may never have heard of them, and why you are now hearing more of the CFD [computational fluid dynamics] firm.At first, they ran a consulting company to manufacturers studying combustion with CFD, such as what happens to the fluids that explode into gasses inside the cylinders of internal combustion engines. (See figure 1.) They would run simulations, but found that the meshing process was a nightmare.

Figure 1Analyzing exploding gasses inside a cylinder

(CFD and FEA [finite element analysis] don't actually analyze fluids-gasses and solids. Instead, the volume is broken into small volumes [cubes] or areas[meshes made of squares], and then the forces acting on each square are calculated and presented as colorful diagrams that show stresses ranging from low [blue] to high [red].)A great deal of the work by CFD companies goes into figuring out how to optimize meshes: smaller mesh sizes return more accurate results but at the cost of much longer processing times. One of today's solutions is to place big meshes in non-critical areas, with much smaller ones in critical areas.The founders of Convergent Science learned that the meshing process is a mess after one client, a large OEM, asked, "If our engineers run this simulation, will we get the same answer?" The answer was "No," because the result was affected by how an engineer sets up the mesh, a manual process. It was after this point that the folks at Convergent Science worked out their solution to the problem, calling it the Adaptive Mesh Refinement system. Here is how it works:

At run time, the software creates the mesh at the interfaces that need it, relaxing it where not needed. "We automate and couple the mesh for each time step," explained director of global marketing Rob Kaczmarek during our interview. "Our special sauce is that meshing and chemistry are fully coupled." Their software today handles spray, turbulence, and boundary temperatures.So on to the reason you are now hearing about Convergent Science. After gaining 90% market share in North America, with customers such as Caterpillar and the big auto makers, they are now expanding into Europe and South East Asia. Overall, sales are growing 30% a year. While the European market grew 120% in the last two years; they expect the Asian market to overtake the North American one in two years.In summary, Converge Science's software...

Q&A

Ralph Grabowski: Does anyone else in FEA or CFD use your flexible mesh approach?Rob Kaczmarek: No one else does it. We have patents on coupled meshing. Others do it through scripting, which pushes, pulls, compresses, and stretches the mesh; but we never do that. Instead, we use our own Grid Convergent Results, where we refine the mesh until the answer is arrived at. This takes out variability from meshing.Grabowski: If you are unique, do you have an direct competitors?Kaczmarek: All competitors use more generalized code, whether ANSYS FLUENT, CFX, STAR-CD, STAR-CCM+, KIVA, Comsol, and so on. The method used in traditional CFD packages is a postdictive process: they get test results, then run CFD analysis and smear the results to get them to match the test data.

We are predictive, in that once we have a grid-convergent result, we can run design alternatives and decide on the best fit for our objectives. We promote using fewer models and more detailed chemistry. When designers use our software, it is easier for them to change geometry. Because the same mesh is always generated, it allows engineering groups in different locations to arrive at the same result.Grabowski: Have anyone offered to buy you out?Kaczmarek: We have had numerous offers, but the co-founders love what they are doing and feel they have even more innovation that they can bring to the industry. Grabowski: What are the sorts of things you are working on these days?Kaczmarek: We are currently working on various new applications areas such as exhaust after treatment, gas turbines, valves, and the most recent, reciprocating compressors. Where the code really shines is when we have complex flows and geometry, moving boundaries, reacting flows, transient flows, or any combination thereof. Grabowski: Tell me about your link to CAD software?Kaczmarek: We import STL files. The traditional drawback to an automated system is that it has to work with watertight geometry, and defeaturing results in an inaccurate model representation. We overcame this challenge by implementing surface healing algorithms from Polygonica, which work stunningly fast. http://www.polygonica.comGrabowski: Might you have plans for a version that runs inside of CAD software?Kaczmarek: This is something we are definitely considering. We have been approached by numerous CAD companies and personally I believe this type of integration is the future. Imagine the impact if a design engineer could run a simple CFD result to predict the best design before sending it over for validation to the testing and CFD engineers. https://convergecfd.com

And One More Thing...

Pictorex last week released their Artisan rendering add-on for BricsCAD V16. To generate photo-realistic images from 3D models, Artisan includes materials and lighting setups. See figure 2. The software is delivered and supported by a worldwide network of resellers, as well as being available through the BricsCAD on-line store. http://www.pictorex.com

Figure 2BricsCAD architectural model rendered by Pictorex Artisan

Sponsor: Okino Graphics

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